Public policy and cost/benefit pressures have created an increasing desire to reduce the amount of polluting gases released by industrial processes. As a result, there has been a drive to find ways of decreasing pollution by modifying industrial processes.
In the petroleum refining industry, fluid catalytic cracking (FCC) of hydrocarbons is a commonly used petroleum refining method. In an FCC process, catalyst particles (inventory) are repeatedly circulated between a catalytic cracking zone and a catalyst regeneration zone. In regeneration, coke deposits (from the cracking reaction) on the catalyst particles are removed at elevated temperatures by oxidation. The removal of coke deposits restores the activity of the catalyst particles to the point where they can be reused in the cracking reaction.
While FCC processes are efficient from the point of catalyst use, the regeneration step typically results in the evolution of undesirable gases such as SO.sub.x, CO, and NO.sub.x. Various attempts have been made to limit the amounts of these gases created during the FCC regeneration step or otherwise to deal with the gases after their formation. Most typically, additives have been used either as an integral part of the FCC catalyst particles themselves or as separate admixture particles in the FCC catalyst inventory in attempts to deal with these problematic gases. For example, magnesium aluminate spinel additives are often used to prevent or minimize emission of SO.sub.x from the regenerator. Various noble metal catalysts have been used to minimize the emission of CO from the regenerator.
Unfortunately, the additives used to control CO emissions typically cause a dramatic increase (e.g., 300%) in NO.sub.x evolution from the regenerator. Some of the spinel-based (SO.sub.x reduction) additives act to lessen the amount of NO.sub.x emission, but with limited success. Thus, there remains a need for more effective NO.sub.x control additives suitable for use in FCC processes.